1. Field of the Invention
The field of the invention relates generally to the control of operational modes of combustion engines. More particularly, the invention relates to control of an advanced concept engine (ACE) using flexible valve and injection events on a per cylinder basis.
2. Related Art
Control of internal combustion engines has received substantial attention in the past several decades. Compression and spark ignition engine designs have attempted to achieve increased flexibility of engine operation. A plethora of designs and patents have been directed to independent intake and exhaust valve actuation and electronic fuel injection. Many of these are directed to computers and feedback systems for controlling engine timing. Systems using independent valve actuation and electronic fuel injection have been conceived to perform engine operational modes not attainable by cam-based engines. However, the embodiments of the instant invention use fully flexible valve and injection events to achieve mixed mode engine operation by varying the order of events on a per cylinder basis.
The above systems that use independent valve actuation and electronic fuel injection employ several methods for valve and injector actuation. Electronically or computer controlled solenoids, electromagnetic transducers and piezoelectric stacks are used for direct actuation. Alternatively, solenoids, transducers and/or stacks are used to control hydraulic valves which in turn actuate cylinder valves and injectors. The opening and closing of valves and injectors in camless systems is typically controlled as a function of some engine parameter such as speed or angular position of the crankshaft.
One example of a dual exhaust valve actuation system is disclosed in GB 2213873A. Two electronically controlled electromagnetic valves are used to switch hydraulic pressure, which in turn acts against the valve springs for counter biasing of the valves. GB 2213873A discloses early exhaust valve opening in order to increase the energy supplied to the turbocharger and thereby reduce turbo lag. A common technique for engine braking is also discussed in GB 2213873A. The exhaust valves are opened at top dead center to prevent energy recovery during the downward stroke of the engine. Moreover, operation of a four stroke engine in two stroke mode is believed to enhance engine braking.
Independent opening and closing of intake and exhaust valves is disclosed in U.S. Pat. No. 4,009,695 to Ule. Ule discloses four hydraulic actuation embodiments. One embodiment describes a pair of rotary hydraulic controlled valves which permit independent timing of intake and exhaust valves. However, as in conventional cam driven valve engines, Ule's system repeats the sequence or order of cylinder firing events for each like valve. Although the ordering of cylinder events are the same for each cylinder, Ule's system provides adaptable timing of intake and exhaust opening and closing. Ule further teaches control of cylinder charge volume by delayed closing of the intake valves. Ule attempts to minimize hydrocarbon emissions due to misfiring by preventing the formation of an intake vacuum.
A bistable electromechanical transducer is taught in U.S. Pat. No. 4,794,890 to Richeson. Richeson's device includes a moving armature controlled by a latching permanent magnet and an electromagnetic repulsion unit for slowing valve motion near extreme valve-open and valve-closed positions. The device is designed for rapid valve opening and closing, i.e., short transition times between stable states. Like other camless systems, the actuation is independent of the engine speed. The valve timing, which is the point within the cycle when opening and closing starts, is also selectable.
The Richeson patent addresses various operational advantages due to electronic control of the electromechanical valve actuator. Exposure of the cylinders to the atmosphere during nonuse is prevented by closing all valves. A cold weather starting sequence begins with the exhaust valves closed and the intake valves open for compressionless cranking until a suitable speed is reached for starting. Spark ignition engine deceleration is accomplished by turning off cylinders by closing selected valves. Engine braking is done by changing valve timing to operate in a compression mode, as discussed above.
Examples of piezoelectric valve actuators are shown in U.S. Pat. Nos. 4,466,390 to Babitzka et al. and 4,593,658 to Moloney. Babitzka et al. disclose the addition of a piezoelectric stack to a cam driven valve. The stack is coupled with a hydraulic system to achieve shortened valve-open time modes. The Moloney patent is directed to a camless system which uses a piezoelectric stack coupled to an amplifying lever arm for direct actuation of a valve.
U.S. Pat. No. 3,589,345 to Benson, U.S. Pat. Nos. 4,499,878 and 4,649,886 to Igashira et al., 3,927,652 to O,Neill, 4,180,022 to Khair et al. and 4,730,585 to Abe et al. teach piezoelectric stack actuated fuel injectors.